Document CI / Devop pipelines

[SteveMacenski]

• [ ] Dockerhub: What files are used and when, what triggers builds, how are these images used, dummy files, any important details to mention like the ignoring builds on failure to keep ros2 current, etc
• [ ] CircleCI: General pipeline, role of different stages, where caching occurs and how to break it, any important details to mention
• [ ] Dockerfiles: source, release, and main repo dockerfile roles and uses
• [ ] updates required between distributions
• [ ] general pipeline diagram
• [ ] code coverage pipeline